1. Field of the Invention
This invention relates to structures for motorcycle swingarms and the like.
2. Description of the Prior Art
As is well known, the swingarm of a motorcycle undergoes considerable stress under certain conditions. Thus, the ends of the arms of the swingarm are subjected to torquing during sharp turns and skids, and particularly in rough terrain. In swingarm structures heretofore known, the resultant stresses are manifested in structural failures at various points, e.g., the ends of the arms and the junctions of the arms and the curved yokes to which they are welded.
Typically, known swingarms have two arms formed of steel tubes of rectangular or circular cross-section, which at one end are welded to the ends of the legs of a curved or generally U-shaped yoke member. The yoke has a transverse bore, which may be constituted of a bearing sleeve welded to the yoke, to facilitate mounting the swingarm on a pin secured to the frame of the motorcycle. The pin on which the swingarm pivots is forward of the rear wheel, with the arms straddling the wheel and the yoke being clear of the wheel. The rear ends of the arms have weld connections to the ends of respective short, slotted plates which are secured to the ends of the rear axle.
The slotted plates may be made of laminated steel sheets, and such plates readily tear and/or bend after repeated stressing. Further in this regard, repeated stressing of known swingarms shows up as fractures at the junctures of the arms and the ends of the yoke; fractures at the junctures of the arms and the slotted plates; and bending and/or collapsing of the arms and slotted plates. Also, the ends of the tubular arms readily compress and bend when the chain is derailed and catches the shock mount following loosening of the axle. Loosening of the axle nut occurs with vibrations, and compressing of the slotted plates secured to the axle, permitting the shock mount to be caught be the chain and resulting in bending of the axle and the tubular arms.